<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>mainPage</title>
</head>
<style>
  .iframe-container{
    width:400px;
    height:500px;
  }
</style>
<body>
  <div>mainPage</div>
  <iframe src="./one.html" class="iframe-container" frameborder="1"></iframe>
  <iframe src="./three.html" class="iframe-container" frameborder="1"></iframe>
  <iframe src="./two.html" class="iframe-container" frameborder="1"></iframe>
  <script>
    console.log('mainPage')
  </script>
</body>
</html>